1. Field of the Invention
The present invention relates generally to vertical processing vessels, which are commonly referred to as shaft or vertical kilns, shaft furnaces or shaft generators, depending upon the process for which the vessel is being used, and more particularly, to a removal grate for use in such vessels.
2. Descriptions of the Prior Art
A common form of processing equipment found in diverse industrial applications is a vertical vessel, having a gravity flow of particulate solids from an upper feed to a lower discharge. Commonly, such vessels are called shaft or vertical kilns, shaft furnaces, shaft generators and the like, depending upon the application and particular type of material being treated. Such vessels have been found useful for burning or calcining treatments such as the calcining of various types of materials to produce lime, coking coal, burning magnesite and/or dolomite, retorting oil shale, etc. Such vessels commonly include a vertical vessel shell, means for uniformly feeding granular or pulverulent material across the lateral extent of the vessel, a lower discharge means for providing a uniform discharge of the solid material from the vessel shell and some means for introducing treating fluids into the solids so that the solid material is treated in accordance with the predesigned process. One of the major problems encountered in this type of vessel is the requirements for the uniform flow of solids across the lateral extent of the vessel from its top to its bottom so as to provide uniform treatment of all of the solid particles passing through the vessel.
In order to accommodate the above problem, many such vessels are rectangular in cross-section, as it is easier to uniformly distribute fluids across a four-sided cross-section. Some vessels are circular in cross-section, but it is difficult to control uniform movement of the particulate material through the vessels.
The need to uniformly distribute the particles across the lateral cross-section of the vessel is important due to the fact that the material being processed typically is crushed, and therefore is presented in a variety of sizes, which are fed through the top of the vessel. The particles are typically centrally fed through the top of the vessel, and a certain amount of segregation automatically occurs with the larger particles, usually migrating to the periphery of the vessel, while the smaller particles concentrate near the center of the vessel. This is due to the natural angle of repose of the material as it accumulates in a feed hopper.
There are several features of a vessel that have an effect on the flow patterns of the particulate matter through the vessel, as well as the treating fluids. As mentioned previously, as material is centrally deposited into a vessel, the larger particles tend to migrate radially outwardly at a faster rate than the smaller particles, and accordingly, systems have been developed for introducing the particulate matter to the vessel in a manner to avoid this known phenomenon of segregation. An example of such a system is disclosed in U.S. Pat. No. 3,071,230, issued to Brakel, et al. on Jan. 1, 1963. This patent uniformly distributes the inflowing particulate matter across the lateral cross-section of the vessel to minimize the angle of repose problem.
It will also be appreciated that, if the material is not removed from the bottom of the vessel in a substantially uniform cross-sectional manner, the flow rate of the particulate matter through the vessel will vary across the cross-section of the vessel. Accordingly, systems have been developed and employed for removing the particulate matter from the bottom of the vessel in as uniform a manner as possible, so as to maintain a uniform cross-sectional flow of the particulate matter through the vessel. Examples of such devices for regulating the uniform withdrawal of particulate material from the vessel are shown in my U.S. Pat. Nos. 3,401,922, issued Sep. 17, 1968, and U.S. Pat. No. 3,373,982, issued Mar. 19, 1968, and Brakel, et al.'s U.S. Pat. No. 3,027,147, issued on Mar. 27, 1962. These patents are each directed to grate systems for uniformly removing particulate matter from a cylindrical vessel. Removal grate systems vary to some degree, dependent upon the cross-sectional dimension of the vessel and, for example, a removal grate system disclosed in my U.S. Pat. No. 5,210,962, issued May 18, 1993, was designed primarily for vessels that are greater than seven and one-half feet in diameter.
It is to provide a removal grate system for vessels of relatively small size that the present invention was developed.